Hyperpolarization and increased free calcium in acetylcholine-stimulated endothelial cells.

In freshly harvested aortic endothelial cells from rabbits, some cellular events associated with stimulation by acetylcholine (ACh) were analyzed. ACh (3 microM) induced a transient hyperpolarization of 8.3 +/- 2.5 mV, which peaked within 3-5 s and subsequently declined with a similar time course. Hyperpolarization was caused by a transient Ca2+-dependent outward current (IoACh), which was mainly carried by K+. ACh (3 and 10 microM) also evoked transient dose-dependent increases in the intracellular free Ca2+ concentration (Ca2+i). Pretreatment with atropine (1 and 3 microM) abolished both responses to ACh, the increase in Ca2+i as well as the transient outward current. It is concluded that IoACh and the rise in Ca2+i are two manifestations of muscarinic receptor stimulation. The rise in Ca2+i might be the primary event, leading to secondary membrane hyperpolarization.